1. Technical Field
This invention relates to constant velocity joints of the Rzeppa type and more particularly to those for use in front wheel drive vehicle applications.
2. Related Art
Prior art constant velocity universal joints are known from U.S. Pat. No. 2,046,584 issued Jul. 7, 1936 to A. H. Rzeppa. So-called xe2x80x9cRzeppaxe2x80x9d universal joints include an outer race, an inner race, and a plurality of balls retained in each of the races in a pair of opposed arcuate groove sets formed lengthwise of the respective inner and outer races. A cage receives the balls. In a Rzeppa universal joint, the lengthwise centers of the outer race and inner race grooves are offset by substantially equal amounts on the opposite sides of a central plane of the joint, such that the joint will operate at a constant velocity through a wide range of joint angles. While suitable for their intended purpose, in present day applications the degree of angulation required of such joints can be so great that when the balls travel to the inward closed end of the joint, there is inadequate groove depth of either the outer race groove or inner race groove to properly support the balls under heavy torque loads. Such insufficient support can produce undesired large contact stresses between the balls and the grooves at high joint angles.
U.S. Pat. No. 3,879,960 discloses a joint where the open portion of the outer race grooves and the closed portion of the inner race grooves are made straight to accommodate a large joint angle while containing the balls. However, the outer race grooves at the closed end still have a shallow depth as in a conventional xe2x80x9cRzeppaxe2x80x9d joint and the inner race groove at the closed end tends to get shallower than the conventional xe2x80x9cRzeppaxe2x80x9djoint because of the straight groove configuration.
U.S. Pat. No. 4,589,857 discloses a joint where the centers of the outer and inner race spherical surfaces are offset by an equal amount on opposite sides of the central plane of the joint, and further where the groove centers of the inner and outer race are offset. Such a configuration provides only a modest gain in groove depth at the closed end while sacrificing cage web strength.
It is an object of the present invention to improve upon such joints to provide both high angularity and strength to the joint.
A constant velocity joint constructed according to the invention includes an outer race having an inner partial spherical concave joint surface disposed about a longitudinal axis of the outer race. A first plurality of circumferentially spaced grooves are formed in the joint surface of the outer race and extend generally longitudinally of the outer race between an open end of the outer race and a closed end. An inner race is disposed in the outer race and has an outer partial spherical convex joint surface disposed about a longitudinal axis of the inner race. A second plurality of circumferentially spaced grooves are formed in the joint surface of the inner race and extend generally longitudinally of the inner race between the open and closed ends of the outer race. Each of the grooves of the second plurality are arranged opposite a corresponding one of the grooves of the first plurality to define a plurality of paired ball groove sets. A plurality of torque-transmitting balls are disposed in the plurality of ball groove sets for movement therealong during relative angulation of the inner and outer races. A ball cage is disposed between the inner race and the outer race and is formed with a plurality of windows supporting the balls in a common ball plane during movement of the balls along the groove sets. The ball cage has an outer convex partial spherical joint surface constrained against relative axial movement by the inner joint surface of the outer race. The ball cage has an inner concave partial spherical joint surface constrained against relative axial movement by the outer joint surface of the inner race. Each groove of each ball groove set has an associated lengthwise extending groove plane. The groove planes of the grooves of each of the ball groove sets are disposed in transverse crossing relation to one another.
The invention has the advantage of providing a fixed center, non-stroking universal joint capable of achieving high joint angulation with exceptional support of the balls at the closed end of the joint. A joint constructed according to the invention is capable of achieving a joint angle of 55xc2x0, whereas a conventional xe2x80x9cRzeppaxe2x80x9d joint is limited to joint angles of about 46xc2x0. Moreover, the cross-groove joint constructed according to the invention provides substantially greater groove depth at the closed end of the joint than that of the xe2x80x9cRzeppaxe2x80x9d joints for proper support of the balls at the high angles, without sacrificing the strength of the ball cage.
The invention has the further advantage of being simple to manufacture and of offering a variety of groove configuration alternatives which achieve the stated objectives of high joint angulation and excellent ball support at such high angles.
According to further advantages, the joint construction of the present invention provides a large groove depth at the open end of the outer race which remains uniform to the closed end. A characteristic ball center motion relative to cage window enables an increase in the cage internal diameter. Accordingly, the depth of the groove at the closed end of the inner race can also be adjusted to an appropriate degree by increasing the inner race sphere diameter.
According to a particular embodiment of the invention, the central line of each groove is a combination of an arc and a tangent straight line. At zero joint angle, the central planes of each groove pair are symmetrically inclined from the joint axis in the radial direction to ensure smooth angulation and constant velocity of the joint.
According to further embodiment, the groove pairs are either continuously curving or are substantially linear along their lengths to alter the characteristics of the joint while achieving the same objectives discussed above.